Gazebo first load slow to load in container (controller spawner fails)?

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Hi everyone. I'm trying to spin up a few containers that will launch a simulation of a UR5e in Gazebo. When I run the container and launch my launch file, the controller spawner complains and ultimately fails to find the Gazebo interface. The odd thing is if I kill the roslaunch command and do it again, everything runs fine. I hypothesize that gazebo needs to initialize or something and takes longer the first time it comes up. I tried a bash script that runs the roslaunch, then kills it x seconds later and runs again, but it doesn't feel right.

Is my hypothesis correct? Is there a way to wait for gazebo to be ready in a launch file?

Log file is here, but this is the first relevant error, I think:

0.000000000 WARN /controller_spawner [spawner:138(main)] [topics: /clock, /rosout] Controller Spawner couldn't find the expected controller_manager ROS interface.

I'm using the image here: osrf/ros:melodic-desktop-full which includes Gazebo 9

To reproduce, have docker installed on a host and run:

docker run -it jdekarske/homestri-remote-experiment:latest

Then, in the container run:

roslaunch experiment_world main_experiment.launch rviz_gui:=false gazebo_gui:=false

Github Repo

Thank you for any help :)